1. Field of the Invention
The present invention relates to a time switch device for a X-ray diagnostic apparatus, in particular for the preparation of a dental exposure, having a rotary knob for setting the exposure time, a time scale concentrically arranged relative to the knob, a symbol carrier concentrically arranged to the knob and adjustable in relative positions of rotation relative to the time scale and the knob. The symbol carrier has symbols of the objects being X-rayed arranged thereon one relative to the other at such a spacing relative to each other so that upon setting one of the symbols to the exposure period associated therewith, the other symbols will be located opposite their respective associated exposure periods on the time scale.
2. Prior Art
A time switch device having a rotatable knob, a scale carrier concentrically arranged relative to the knob and a symbol carrier concentrically arranged to the knob and movable relative to the time scale and the knob is disclosed in a co-pending U.S. patent application Ser. No. 631,612, filed Mar. 13, 1975, which issued as U.S. Pat. No. 4,013,036 and corresponds to German patent application No. P 24 61 263.3. The symbol carrier has symbols of the object to be X-rayed arranged thereon one relative to the other with a selected spacing therebetween so that upon setting one of the symbols to the exposure period associated therewith, the other symbols will be located opposite their respective associated exposure periods on the time scale. With this device, the exposure data can be adjusted in a very simplified manner. It is necessary to first set the symbol carrier by rotating it relative to the knob and time scale so that one of the symbols is at the desired exposure time or period for the object represented by that symbol. With such adjustment of the symbol carrier, each of the other symbols will be located at the desired exposure period or time for their respective objects. During exposure, a mark on the knob is rotated to be aligned with the desired symbol of the object to be X-rayed and then the timer will provide the correct amount of exposure. This time switch device permits the selecting of the exposure time on the basis of the object symbol.